There are too many indexes in the manual of every DVR.
But the most important information for users is:
Display definition
D1 (704*576 PAL), CIF(352*288 PAL), QCIF,QVGA etc.
Record definition
D1 (704*576 PAL), CIF(352*288 PAL), QCIF,QVGA etc.
Hard Disk interface
SATA or IDE, usually1 to4
Audio interface
as you want
Encode protocol
H.264 or MPEG-4
D1 definition video looks like DVD, and CIF difinition video looks like VCD.
H.264 is better than MPEG-4 because H.264 is a ITU-T protocol,and the efficency of encoding is better than MPEG-4, it means the same definition video file on your disk is smaller when it is encoded in H.264.
The maximal frame per second of PAL is 25, and NTSC is 30, the difference between PAL and NTSC is not only FPS, but definition and other factors.
The FPS of a DVR is narration of the capacity of processor.Users need not care about so many index, just set your DVR at PAL,D1,25FPS,and your TV and DVD must be set to PAL too, then you will be pleased to hava a not bad video surveillance system for individual use.